The use of telephones for communication is well known. Telephone communication is conventionally accomplished with communication networks that provide point-to-point audio communication between users connected to the network. A network includes equipment for switching incoming audio signals to outgoing audio signals based on pre-defined protocols and numbering systems. The sophistication of the network itself can range from simple, point-to-point links, to vast networks connecting millions of users by underseas cables, satellites or radio frequency transmission.
Although networks are becoming increasingly complex, improvements in the connection between a user instrument and the network are conspicuously absent. Paired copper cables have been employed for many years as the primary connection means between network, an RJ-11 wall jack in many cases, and the instrument itself. The transmission distance supported by copper cable is limited, as is its immunity to electromagnetic noise. The security of copper cable is also weak; mere exposure of the copper medium to a high-impedance signal monitor can defeat the privacy of a communication.
Certain applications of telephone communication require more than one instrument at a location, or the simultaneous communication of digital data. Current paired cable installations can only support a single, duplex communication link. Additional cables are necessary to support additional instruments or devices.
Cordless and cellular telephones have been introduced as alternate communication systems between user instruments and the network. Though effective in their use of radio frequency transmissions to free users from cable connections, the distance over which such links operate are limited. Such transmissions are also extremely susceptible to noise and are less secure than their cable counterparts because of their omni-directional, free-space transmissions.
An example of a current system requiring features not available with the aforementioned transmission media is the INMARSAT satellite transceiver system. The communication network, as implemented in this system, includes ground-based transceivers with antennas for communicating via the satellite link. The actual user instruments, however, are conventional telephone handsets, and are connected to the ground-based transceiver using standard paired copper cabling. Two telephone instruments near an operator are required, as is a third device for communicating digital control information to the transceiver. The distance between the transceiver and the remote site where operators are located is currently limited to 500 feet. The extension of this distance between the three mixed analog/digital communication devices and the transceiver beyond 500 feet is desirable, as is noise free, secure, single medium communication.
A need therefore exists for a communication medium which is capable of extending the distance between a conventional telephone instrument and its connection to a conventional communication network. The medium must accommodate mixed modes of communication (analog/digital) on multiple independent channels. Further, the medium must be secure, immune from noise, easily installed and must operate transparently to existing networks and instruments.